1. Field of the Invention
The present invention relates to a dishwasher, and more particularly, to a dishwasher with an improved structure for exactly estimating a pollution level of wash water.
2. Discussion of the Related Art
In general, a dishwasher is an apparatus for automatically washing dishes. Owing to the functions of washing, rinsing, drying, and storing dishes, the dishwasher greatly reduces housework.
A washing method of the dishwasher is divided into a shower type and a supersonic type. The shower type dishwasher is normally employed for domestic use. The shower type dishwasher washes dishes by spraying hot water on dishes put in a dish basket, the water in which detergent dissolved. A method for spraying water includes spraying using a propeller, and boring a plurality of holes on a pipe and rotating the pipe.
Referring to FIG. 1, structural elements of a conventional dishwasher will be briefly described as follows. The conventional dishwasher includes a water collection part 1, a motor 2 for driving the water collection part 1, and upper and lower washing parts 3 and 4 through which wash water flowed in from the water collection part is sprayed.
The water collection part 1 is provided with a main water collection part 1a for receiving water from outside, or collecting and discharging polluted water after washing. A channel forming part 1b having a channel formed thereat for moving wash water to upper and lower washing part is provided at an upper part of the main water collection part 1a, the wash water circulating in the dishwasher. A filtering part 1c for removing contaminants by filtering the wash water is connected to the channel forming part 1b. 
The motor 2 drives a washing pump for supplying wash water to upper and lower parts 3 and 4 during dishwashing, or provides power for driving a drain pump. The upper and lower washing parts 3 and 4 are places wherein dishwashing is actually performed, and connected to the water collection part through a coupling pipe. A spraying arm (not shown) washes contaminated dishes by spraying wash water supplied from the water collection part 1.
Operation process of the conventional dishwasher will be sequentially described as follows. First, dishes to be washed are put in the dish basket, and an administration is inputted. Then, a predetermined amount of wash water is filled in the main water collection part of the dishwasher through a supply valve connected with the outside of the dishwasher.
Thereafter, the dishwasher heats the supplied wash water by driving a heater, and drives a washing pump by driving a motor. Then, the heated wash water is moved to upper and lower spraying arm through a coupling pipe via the washing pump. The wash water reached to the spraying arm is sprayed through a spraying nozzle so as to remove contaminants on surfaces of the dishes.
After dishwashing, the contaminants and the wash water separated from the dishes are collected at the main water collection part. When the contamination of the wash water is over a predetermined level, the dishwasher discharges wash water mixed with contaminants and is supplied with fresh water from the outside.
When the contamination of the wash water is under the predetermined level, the dishwasher purifies the wash water collected at the water collection part and moves the refreshed water back to the upper and lower parts of the spraying arm via the washing pump. When the washing is terminated, the wash water collected in the main collection part is discharged to the outside through the drain pump, along with the contaminants.
Meanwhile, in the conventional dishwasher, a three-way valve is employed for controlling the direction of the wash water, and normally a solenoid valve is employed. The solenoid valve is automatically opened and closed by the principle of electromagnetic induction, and usually employed for automation of machines or to a safety device.
The conventional dishwasher however has problems as follows. First, in the conventional dishwasher, a channel for measuring contamination of wash water is not separately provided, and the contamination of the wash water is measured on the channel through which the wash water flows to a spraying arm. Accordingly, since a contamination sensor of the conventional dishwasher measures contamination of the wash water flowing at a high speed, there is a problem that the contamination level of the wash water may be inaccurate.
Second, since a channel through which a large amount of wash water passes is formed at the conventional contamination sensor, the size of the contamination sensor itself becomes large, and thus mounting the contamination sensor is complicated.